Method for calibrating ultrasonic characteristics on a wire bonding system

Abstract

A method for calibrating ultrasonic characteristics on a wire bonding system is provided, the method including the steps of: (a) determining a reference ultrasonic characteristic for forming a wire bond, (b) determining a reference non-tacky ultrasonic characteristic that produces a non-tacky wire bond condition, (c) determining a calibrated non-tacky ultrasonic characteristic that produces a non-tacky wire bond condition on a wire bonding system to be calibrated, and (d) determining a calibration factor for the wire bonding system to be calibrated using the reference non-tacky ultrasonic characteristic and the calibrated non-tacky ultrasonic characteristic.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 280,107, filed November 16, 2021, the contents of which are incorporated herein by reference.

[0002] The present invention relates to wire bonding operations, and more particularly to a method for calibrating ultrasonic characteristics on a wire bonding system. [Background technology]

[0003] In semiconductor assembly, wire bonding continues to be a widely used process for providing electrical interconnections within semiconductor packages. A variety of process parameters are utilized in connection with the wire bonding process. For example, ultrasonic energy (and related process parameters) is frequently used to bond wires to a work piece.

[0004] Wire bonding processes are often not repeatable using the same parameters. For example, a given wire bonding system may differ from another wire bonding system. Thus, using the same process parameters (e.g., wire bonding parameters) used in a given wire bonding system may not necessarily result in the same performance (e.g., the same quality wire bonds) in another wire bonding system.

[0005] Furthermore, the same process parameters (e.g., wire bonding parameters) used in the same wire bonding system may not necessarily result in the same performance, for example, when changes are made to the wire bonding system (e.g., new wire bonding tools, new wire spools, changes due to system aging or condition, etc.), the performance (e.g., wire bond quality, etc.) may change even when using the same parameters.

[0006] It would therefore be desirable to provide an improved method for calibrating the ultrasonic characteristics of a wire bonding system. Summary of the Invention [Means for solving the problem]

[0007] According to an exemplary embodiment of the present invention, a method for calibrating ultrasonic characteristics on a wire bonding system is provided, the method including the steps of: (a) determining a reference ultrasonic characteristic for forming a wire bond, (b) determining a reference non-tacky ultrasonic characteristic that produces a non-tacky wire bond condition, (c) determining a calibrated non-tacky ultrasonic characteristic that produces a non-tacky wire bond condition on a wire bonding system to be calibrated, and (d) determining a calibration factor for the wire bonding system to be calibrated using the reference non-tacky ultrasonic characteristic and the calibrated non-tacky ultrasonic characteristic.

[0008] According to an exemplary embodiment of the present invention, a method for calibrating ultrasonic characteristics on a wire bonding system is provided, the method including the steps of: (a) determining a reference ultrasonic characteristic for forming a wire bond, (b) determining a reference out-of-tolerance ultrasonic characteristic that produces an out-of-tolerance wire bond condition, (c) determining a calibration out-of-tolerance ultrasonic characteristic that produces an out-of-tolerance wire bond condition on a wire bonding system to be calibrated, and (d) determining calibration coefficients for the wire bonding system to be calibrated using the reference out-of-tolerance ultrasonic characteristic and the calibration out-of-tolerance ultrasonic characteristic.

[0009] The methods of the present invention may also be implemented as an apparatus (e.g., as part of the intelligence of a wire bonding system) or as computer program instructions on a computer readable medium (e.g., a computer readable medium including a wire bonding program for use in connection with a wire bonding system). [Brief description of the drawings]

[0010] The invention is best understood from the following detailed description when read in conjunction with the accompanying drawings. According to common practice, the various elements of the drawings are not drawn to scale. Rather, dimensions of the various elements have been arbitrarily expanded or reduced for clarity. The figures include: [Figure 1A] 1A-1D are a series of block diagrams illustrating wirebond testing with reference ultrasonic characteristics in accordance with an exemplary embodiment of the present invention. [Figure 1B] 1A-1D are a series of block diagrams illustrating wirebond testing with reference ultrasonic characteristics in accordance with an exemplary embodiment of the present invention. [Figure 1C] 1A-1D are a series of block diagrams illustrating wirebond testing with reference ultrasonic characteristics in accordance with an exemplary embodiment of the present invention. [Figure 1D] 1A-1D are a series of block diagrams illustrating wirebond testing with reference ultrasonic characteristics in accordance with an exemplary embodiment of the present invention. [Figure 2A] 2A-2D are a series of block diagrams illustrating wire bond testing with modified ultrasonic properties in accordance with an exemplary embodiment of the present invention. [Figure 2B] 2A-2D are a series of block diagrams illustrating wire bond testing with modified ultrasonic properties in accordance with an exemplary embodiment of the present invention. [Figure 2C] 2A-2D are a series of block diagrams illustrating wire bond testing with modified ultrasonic properties in accordance with an exemplary embodiment of the present invention. [Figure 2D] 2A-2D are a series of block diagrams illustrating wire bond testing with modified ultrasonic properties in accordance with an exemplary embodiment of the present invention. [Figure 3A] 3A-3D are a series of block diagrams illustrating another modified ultrasonic characteristic wire bond testing in accordance with an exemplary embodiment of the present invention. [Figure 3B] 3A-3D are a series of block diagrams illustrating another modified ultrasonic characteristic wire bond testing in accordance with an exemplary embodiment of the present invention. [Figure 3C] 3A-3D are a series of block diagrams illustrating another modified ultrasonic characteristic wire bond testing in accordance with an exemplary embodiment of the present invention. [Figure 3D] 3A-3D are a series of block diagrams illustrating another modified ultrasonic characteristic wire bond testing in accordance with an exemplary embodiment of the present invention. [Figure 4] 4-5 are a flow diagram illustrating a method for calibrating ultrasonic characteristics in a wire bonding system in accordance with yet another exemplary embodiment of the present invention. [Diagram 5] 4-5 are a flow diagram illustrating a method for calibrating ultrasonic characteristics in a wire bonding system in accordance with yet another exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] As used herein, the term "ultrasonic property" is intended to refer to any variable (e.g., a variable value, a variable percentage, etc.) intended to adjust the ultrasonic output of an ultrasonic transducer on a wire bonding system (e.g., a wire bonding machine). For example, such a property may be an electrical property (e.g., a current, a voltage, a power, etc.). In a specific example, the ultrasonic property is a current value (or a current percentage) configured to be applied to an ultrasonic transducer on a wire bonding system to form a wire bond.

[0012] As will be appreciated by those skilled in the art, a particular ultrasonic characteristic (e.g., current, power, etc.) used in a wire bonding system may be expressed as a predetermined value (e.g., a particular value of milliamps or mA, etc.), a predetermined percentage (e.g., a percentage of a predetermined value, such as a percentage of a reference value), etc. Other methods of expressing such ultrasonic characteristics are contemplated.

[0013] An exemplary aspect of the present invention relates to a calibration method for adjusting ultrasonic properties on a wire bonding system, thereby providing portability of the wire bonding system (e.g., wire bonding equipment), i.e., the on-wire bonding system functionality provides "on-bonder" calibration (e.g., real-time adjustment of one or more bonding parameters, such as ultrasonic properties), to overcome challenges associated with equipment portability (e.g., a given equipment is different from another equipment, conditions change during production on a given equipment, etc.).

[0014] According to an aspect of the invention, reference response data is collected at multiple ultrasonic characteristics (e.g., multiple values ​​and / or rates of current applied to the ultrasonic transducer) to generate a reference ultrasonic characteristic for forming a wire bond (e.g., current level applied to the ultrasonic transducer to form a desired ball bond in a wire loop). This reference response data can be collected, for example, from one or more wire bonding systems or from a single reference wire bonding system. The reference ultrasonic characteristic is generated using the reference response data (e.g., stored in a memory). This reference ultrasonic characteristic is stored (e.g., on a computer included in the wire bonding system, an external computer accessible to the wire bonding system, etc.) as a "golden" value (e.g., an ultrasonic characteristic setting, such as a current setting, configured to be applied to an ultrasonic transducer on the wire bonding system to form a wire bond). In certain examples, the reference ultrasonic characteristic may be stored in a bonding program for a particular application. After the reference ultrasonic characteristic is determined, a reference unacceptable ultrasonic characteristic and a calibration unacceptable ultrasonic characteristic are determined.

[0015] For example, a baseline out-of-tolerance ultrasonic property is determined, where the baseline out-of-tolerance ultrasonic property is a property that results in an out-of-tolerance wire bond condition (e.g., a non-stick wire bond condition, a low shear strength wire bond condition, a low pull strength wire bond condition, and an out-of-tolerance level of wire bond deformation). For example, to determine such a baseline out-of-tolerance ultrasonic property, during the wire bonding operation, an applied ultrasonic property (e.g., an ultrasonic property starting from the baseline ultrasonic property or other value) is incrementally adjusted (e.g., decreased, increased, or both decreased and increased) until an out-of-tolerance wire bond condition occurs, and then the baseline out-of-tolerance ultrasonic property is determined when the out-of-tolerance condition occurs. For example, the incremental adjustment value may be a value and / or percentage of the ultrasonic property (e.g., ultrasonic current level). The baseline out-of-tolerance ultrasonic properties may be stored along with the baseline ultrasonic properties on a computer (e.g., as part of an application-specific bonding program, on a computer local to the wire bonding system, on a remote computer accessible by the wire bonding system, etc.).

[0016] Next, for example, the calibration proceeds to determine a set point (e.g., a value of an ultrasonic characteristic used in another wire bonding system) for the wire bonding system being calibrated. First, a calibration out-of-tolerance ultrasonic characteristic is determined for the wire bonding system being calibrated. The calibration out-of-tolerance ultrasonic characteristic results in an out-of-tolerance wire bonding condition. To determine the calibration out-of-tolerance ultrasonic characteristic, the ultrasonic characteristic (e.g., starting from a reference ultrasonic characteristic or other value) is adjusted incrementally (e.g., 5% increase, 5% decrease, 1 unit increase, etc.) for additional wire bonds until an out-of-tolerance bonding condition occurs. If an out-of-tolerance bonding condition occurs, the corresponding ultrasonic characteristic is recognized as a calibration out-of-tolerance ultrasonic characteristic. Second, a calibration factor for the wire bonding system being calibrated is determined using the reference out-of-tolerance ultrasonic characteristic and the calibration out-of-tolerance ultrasonic characteristic. The calibration factor can be determined by determining the difference between the reference out-of-tolerance ultrasonic characteristic and the calibration out-of-tolerance ultrasonic characteristic. The calibration factor is then used to calculate new settings for the calibrated wire bonding system, for example, the calibration factor can be applied (e.g., as a multiplier) to the reference ultrasonic characteristic.

[0017] The new setpoints may be considered the actual ultrasonic characteristics applied to the wire bonding system being calibrated. However, the process of calibrating the ultrasonic characteristics on the wire bonding system being calibrated may be repeated upon application of a new wire bond and / or following a particular trigger. That is, calibration may be performed on the wire bonding system upon the occurrence of a trigger. Examples of triggers include upon start-up of the wire bonding system (e.g., when a processing program is initially loaded onto the machine), upon replacement of a wire spool on the wire bonding system, upon replacement of a wire bonding tool on the wire bonding system, upon operator request, upon the lapse of a predetermined period of time, upon the lapse of a predetermined number of wire bonds on the wire bonding system, etc.

[0018] Upon the occurrence of a predetermined trigger, a calibration is performed to determine settings for the wire bonding system and / or for a particular application on the wire bonding system.

[0019] An example follows. Assume that a user has a specific wire bonding application. The application has specific requirements, e.g., a specific wire, a specific wire bonding tool, a specific work piece, a specific wire bonding program, a specific set of wire bonding parameters, etc. These application-specific requirements are used to determine the desired ultrasonic properties (e.g., a current value applied to the transducer, a voltage value applied to the transducer, a power value applied to the transducer, etc.). Here, the desired ultrasonic properties (e.g., a reference ultrasonic property, UC REF ) is assumed to be a current of 100mA.

[0020] Each of FIGS. 1A-1D, 2A-2D, and 3A-3D represents a series of tests in which the applied ultrasonic property is adjusted (e.g., decreased) in steps until an unacceptable wire bond condition results. The applied ultrasonic property may be an increment of a reference ultrasonic property. In this example, the reference ultrasonic property is a current of 100 mA. In FIGS. 1A-1D, the reference ultrasonic property is applied to achieve a desired wire bond. In FIGS. 2A-2D, an increment of the reference ultrasonic property is applied, resulting in a qualified wire bond. In FIGS. 3A-3D, another increment of the reference ultrasonic property is applied, resulting in an unacceptable wire bond (e.g., a non-tacky wire bond condition). This example is a simple example having only three test points (i.e., FIGS. 1A-1D, 2A-2D, and 3A-3D), but of course many more test points (with many different increments of the reference ultrasonic property) can be utilized.

[0021] The stepwise adjustment of the applied ultrasonic characteristic (as shown in FIGS. 1A-1D, 2A-2D, and 3A-3D) can be used to determine (i) a reference non-stick ultrasonic characteristic and / or (ii) an out-of-calibration tolerance ultrasonic characteristic. The reference non-stick ultrasonic characteristic may be determined on a reference wire bonding system (or multiple wire bonding systems). Such a reference wire bonding system is shown in FIGS. 1A-1D, 2A-2D, and 3A-3D as reference wire bonding system 100. The out-of-calibration tolerance ultrasonic characteristic is determined on a wire bonding system to be calibrated (sometimes referred to herein as the "actual," "given," or "target" wire bonding system). Such a wire bonding system to be calibrated is shown in FIGS. 1A-1D, 2A-2D, and 3A-3D as reference wire bonding system 100'.

[0022] 1A-1D illustrate free air ball bonding using a reference ultrasonic characteristic (e.g., set point 100 mA). FIG. 1A illustrates a reference wire bonding system 100 including a support structure 102 and a bond head assembly 110. The support structure 102 supports a workpiece 104 including a die 104a attached to a substrate 104b. The die 104a includes a first bonding position 104a1. The bond head assembly 110 includes a transducer 110a that holds a wire bonding tool 108. The wire bonding tool 108 includes a working end 108a. A wire 106 is threaded through the wire bonding tool 108 and includes a free air ball 106a at the working end 108a. The transducer 110a is electrically connected to a computer 112 configured to store data and control the motion (and operation) of the transducer 110a.

[0023] The computer 112 is electrically connected to a detection system 114 that can detect whether the bonded portions of the wires are properly attached to their respective bonding locations (e.g., bond pads, leads, contacts, traces, etc.). For example, wire bonding machines sold by Kulicke and Soffa Industries, Inc. frequently utilize a "BITS (Bond Integrity Test System)" process (i.e., bond integrity test system) in conjunction with such detection systems to ensure that proper wire bonds have been formed. Exemplary details of the above process are disclosed in International Publication No. WO 2009 / 002345, which is incorporated herein by reference in its entirety. The detection system 114 can detect whether the bonded portions of the wires are properly attached to their bonding locations by performing an electrical continuity test. However, it is understood that other types of detection systems can be used (e.g., optical inspection systems for detecting whether portions of the wires are properly attached to their bonding locations, etc.).

[0024] FIG. 1B illustrates the beginning of a bonding process in the wire bonding system 100. In FIG. 1B, the bond head assembly 110 moves downward until the free air ball 106a contacts the first bonding location 104a1 of the die 104a. In FIG. 1C, the free air ball 106a is ultrasonically bonded to the first bonding location 104a1 using a reference ultrasonic characteristic (e.g., 100 mA) to form a bonded ball 106a'. In FIG. 1D, the bond head assembly 110 moves away from the bonded ball 106a'. The detection system 114 is used to verify that the bonded ball 106a' is properly bonded to the first bonding location 104a1 (e.g., determine whether a non-tacky wire bond condition exists, determine whether a low shear strength wire bond condition exists, determine whether a low tensile strength wire bond condition exists, and / or determine whether an unacceptable level of wire bond deformation exists). In FIG. 1D, the desired ball bond is formed using the reference ultrasonic characteristics.

[0025] As discussed above, FIGS. 2A-2D and 3A-3D depict repeated bonding steps at multiple adjustment levels (e.g., increments) of the baseline ultrasonic property (e.g., 1% step decreases, 5% step decreases, 1% step increases, 5% step increases, etc.). That is, the ultrasonic property is iteratively adjusted (e.g., decreased by a predetermined value and / or percentage, increased by a predetermined value and / or percentage, etc.) until an unacceptable wire bond condition is formed. In the example shown in FIGS. 2A-2D, an acceptable ball bond is formed at one adjustment level of the baseline ultrasonic property in FIG. 2D.

[0026] This process is repeated until an out-of-tolerance wire bond condition occurs. FIGS. 3A-3D illustrate the occurrence of such an out-of-tolerance wire bond condition (e.g., the presence of a non-tacky wire bond condition). Assume that in the reference wire bonding system 100, this condition occurs at a 20% reduction (i.e., the out-of-tolerance wire bond condition is reached by applying a current of 80 mA). However, the reference out-of-tolerance ultrasonic property may be expressed in other ways. For example, the reference out-of-tolerance ultrasonic property may be expressed as a percentage of the reference ultrasonic property (i.e., 0.8 * U.C. REF )

[0027] Assume that on a wire bonding system being calibrated (e.g., wire bonding system 100'), this out-of-tolerance wire bond condition occurs at a 25% reduction (i.e., the out-of-tolerance wire bond condition is reached by applying a current of 75 mA). Thus, the out-of-tolerance ultrasonic characteristic may be expressed as a value of the ultrasonic characteristic (e.g., 75 mA). However, the out-of-tolerance ultrasonic characteristic may be expressed in other ways. For example, the out-of-tolerance ultrasonic characteristic may be expressed as a percentage of the reference ultrasonic characteristic (i.e., 0.75 * U.C. REF )

[0028] It is understood that these steps may be repeated over multiple cycles to determine the exact reference and / or calibrated out-of-tolerance ultrasonic characteristic, i.e., a certain percentage of out-of-tolerance wirebond conditions may occur during calibration (e.g., for a given adjusted ultrasonic characteristic), before the reference and / or calibrated out-of-tolerance ultrasonic characteristic is determined.

[0029] For example, when determining a calibrated out-of-tolerance ultrasonic characteristic, an iterative process may be performed in which a certain percentage of out-of-tolerance wirebond conditions must occur before an out-of-tolerance result is determined. For example, assume 20 wirebonds are inspected at each value of an applied ultrasonic characteristic. In this case, three out-of-tolerance wirebond conditions (3 out of 20) may be required before an out-of-tolerance result is determined. Of course, this is merely an example. Assume the out-of-tolerance result occurs at a current level of 75 mA.

[0030] After the reference out-of-tolerance ultrasonic characteristic and the calibrated out-of-tolerance ultrasonic characteristic are determined, a calibration factor is determined. The calibration factor is used to determine the ultrasonic characteristic settings of the wire bonding system being calibrated. The calibration factor can be thought of as the difference between the reference out-of-tolerance ultrasonic characteristic and the calibrated out-of-tolerance ultrasonic characteristic. The calibration factor may be provided as a percentage. In the above example, the reference out-of-tolerance ultrasonic characteristic is 0.8. * U.C. REF , and the calibration tolerance range of ultrasonic characteristics is 0.75 * U.C. REF In this case, the calibration factor is 5% (0.05 * U.C. REF ).

[0031] A calibration factor can be used to determine the ultrasonic property setting of the wire bonding system to be calibrated. In the above example, the reference ultrasonic property is a current of 100 mA. If the calibration factor is 5% for the wire bonding system to be calibrated, the ultrasonic property setting of the wire bonding system can be determined by reducing the reference ultrasonic property by 5%. Therefore, the ultrasonic property setting can be considered to be 95 mA.

[0032] 4-5 are flow diagrams illustrating a method for calibrating ultrasonic properties on a wire bonding system. As will be appreciated by those skilled in the art, certain steps included in the flow diagrams may be omitted, certain additional steps may be added, and the order of steps may be altered from the order shown, all within the scope of the present invention.

[0033] Referring to FIG. 4, in process 400, a reference ultrasonic characteristic (e.g., a current value configured to be applied to an ultrasonic transducer on a wire bonding system) for forming a wire bond is determined. For example, process 400 can include determining the reference ultrasonic characteristic on a reference wire bonding system (or multiple reference wire bonding systems) using an application-specific member. Examples of application-specific members include at least one of (i) a wire, (ii) a wire bonding tool, and (iii) a workpiece. For example, process 400 can include determining the reference ultrasonic characteristic on the reference wire bonding system(s) using an application-specific wire bonding program. For example, process 400 can include determining the reference ultrasonic characteristic on the reference wire bonding system(s) using application-specific wire bonding parameters.

[0034] In step 402, a reference non-tacky ultrasonic characteristic that produces a non-tacky wire bond condition is determined (e.g., on a reference wire bonding system). For example, step 402 includes determining the reference non-tacky ultrasonic characteristic by incrementally adjusting (e.g., decreasing) an applied ultrasonic characteristic during a wire bonding operation until a non-tacky wire bond condition occurs. The reference non-tacky ultrasonic characteristic can be considered to be the applied ultrasonic characteristic that produces a non-tacky wire bond condition. For example, with respect to step 402, if a predetermined percentage of the wire bonds tested with the applied ultrasonic characteristic do not adhere to their respective bond locations, a non-tacky wire bond condition may have occurred. FIGS. 2A-2D and 3A-3D illustrate incremental adjustments that produce acceptable wire bonds (FIG. 2D) and non-tacky wire bonds (FIG. 3D). The reference non-tacky ultrasonic characteristic can be determined, for example, using the value (or percentage) of the reference ultrasonic characteristic that corresponds to FIG. 3D (indicating the occurrence of a non-tacky wire bond).

[0035] In step 404, a calibration non-stick ultrasonic characteristic of the wire bonding system being calibrated is determined. The calibration non-stick ultrasonic characteristic produces a non-stick wire bond condition. For example, step 404 includes determining the calibration non-stick ultrasonic characteristic by incrementally adjusting an applied ultrasonic characteristic during a wire bonding operation until a non-stick wire bond condition occurs. The calibration non-stick ultrasonic characteristic can be considered to be the applied ultrasonic characteristic that produces the non-stick wire bond condition. For example, with respect to step 404, if a predetermined percentage of the wire bonds tested with the applied ultrasonic characteristic do not adhere to their respective bond locations, a non-stick wire bond condition may have occurred. As discussed above, FIGS. 2A-2D and 3A-3D illustrate incremental adjustments that produce acceptable wire bonds (FIG. 2D) and non-stick wire bonds (FIG. 3D). A calibrated non-tacky ultrasonic characteristic can be determined, for example, using the value (or percentage) of the reference ultrasonic characteristic corresponding to FIG. 3D (indicating the occurrence of a non-tacky wire bond).

[0036] The reference non-tacky ultrasonic signature and the calibration non-tacky ultrasonic signature are used to determine a calibration factor for the wire bonding system being calibrated in step 406. For example, step 406 can include determining a difference between the reference non-tacky ultrasonic signature and the calibration non-tacky ultrasonic signature.

[0037] Referring to FIG. 5, in process 500, a reference ultrasonic characteristic (e.g., a current value configured to be applied to an ultrasonic transducer on a wire bonding system) for forming a wire bond is determined. For example, process 500 can include determining the reference ultrasonic characteristic on a reference wire bonding system (or multiple reference wire bonding systems) using an application-specific member. Examples of application-specific members include at least one of: (i) a wire, (ii) a wire bonding tool, and (iii) a workpiece. For example, process 400 can include determining the reference ultrasonic characteristic on the reference wire bonding system(s) using an application-specific wire bonding program. For example, process 500 can include determining the reference ultrasonic characteristic on the reference wire bonding system(s) using application-specific wire bonding parameters. For example, process 500 can include determining the reference ultrasonic characteristic on the reference wire bonding system(s) using application-specific wire bonding parameters.

[0038] In step 502, a baseline out-of-tolerance ultrasonic characteristic that results in an out-of-tolerance wire bond condition is determined (e.g., on a baseline wire bonding system). Examples of an out-of-tolerance wire bond condition include one or more of: (i) a non-tacky wire bond condition; (ii) a low shear strength wire bond condition; (iii) a low tensile strength wire bond condition; and (iv) an unacceptable level of wire bond deformation. For example, step 502 may include determining the baseline out-of-tolerance ultrasonic characteristic by incrementally adjusting (e.g., decreasing) an applied ultrasonic characteristic during a wire bonding operation until an out-of-tolerance wire bond condition occurs. The baseline non-tacky ultrasonic characteristic may be considered to be the applied ultrasonic characteristic that results in an out-of-tolerance wire bond condition. For example, with respect to step 502, an out-of-tolerance wire bond condition may occur if a predetermined percentage of the wire bonds tested with the applied ultrasonic characteristic are out-of-tolerance based on a predetermined criterion. 2A-2D and 3A-3D show incremental adjustments that result in an acceptable wire bond (FIG. 2D) and an unacceptable wire bond (FIG. 3D). The baseline out-of-tolerance ultrasonic property can be determined, for example, using the value (or percentage) of the baseline ultrasonic property corresponding to FIG. 3D (indicating the occurrence of an unacceptable wire bond).

[0039] In step 504, a calibrated out-of-tolerance ultrasonic characteristic of the wire bonding system being calibrated is determined. The calibrated out-of-tolerance ultrasonic characteristic produces an out-of-tolerance wire bond condition. For example, step 504 includes determining the calibrated out-of-tolerance ultrasonic characteristic by incrementally adjusting (e.g., decreasing, increasing, decreasing and increasing) an applied ultrasonic characteristic during a wire bonding operation until an out-of-tolerance wire bond condition occurs. The calibrated out-of-tolerance ultrasonic characteristic may be considered to be an applied ultrasonic characteristic that produces an out-of-tolerance wire bond condition. For example, with respect to step 504, if a predetermined percentage of the wire bonds tested with the applied ultrasonic characteristic are out of tolerance based on a predetermined criterion, an out-of-tolerance wire bond condition may have occurred. As discussed above, FIGS. 2A-2D and 3A-3D illustrate incremental adjustments that produce acceptable wire bonds (FIG. 2D) and out-of-tolerance wire bonds (FIG. 3D). An out-of-calibration tolerance ultrasonic characteristic can be determined, for example, using the value (or percentage) of the baseline ultrasonic characteristic corresponding to FIG. 3D (indicating the occurrence of an out-of-tolerance wire bond).

[0040] The reference out-of-tolerance ultrasonic characteristic and the calibration out-of-tolerance ultrasonic characteristic are used to determine a calibration factor for the wire bonding system being calibrated in step 506. For example, step 506 can include determining a difference between the reference out-of-tolerance ultrasonic characteristic and the calibration out-of-tolerance ultrasonic characteristic.

[0041] The methods of Figures 4 and 5 can be further expanded to include additional steps such as determining ultrasonic property settings for a wire bonding system that is calibrated using the calibration coefficients, and forming a wire bond (e.g., a first bond of a wire loop, a bump, a ball bond of a vertical wire, etc.) using the ultrasonic property settings.

[0042] The calibration described herein solves the problems of portability between equipment and material variations (e.g., wire, wire bonding tool, workpiece holder, workpiece variations) without the use of metrology equipment external to the bonder. Such novel calibrations can be used to account for the specific wire bonding tool (e.g., capillary, etc.), wire, workpiece holder, and workpiece (e.g., die, substrate, etc.) used in a wire bonding application.

[0043] Although the present invention has been shown and described primarily in connection with a first bond (e.g., a ball bond) of a wire loop, the present invention is not so limited. The teachings of the present invention may be applied to any bonded portion of a wire, including a second bond of a wire loop, a stitch bond, a bonding ball, a bump, a ball bond of a vertical wire, and the like.

[0044] Although the invention has been illustrated and described herein with reference to specific embodiments, it is not intended that the invention be limited to the details shown, but rather various changes in the details may be made within the scope of the claims and the equivalents thereof without departing from the invention.

Claims

1. 1. A method for calibrating ultrasonic characteristics on a wire bonding system, comprising: (a) determining a reference ultrasonic characteristic for forming a wire bond; (b) determining a baseline non-tacky ultrasonic characteristic that produces a non-tacky wire bond condition; (c) determining a calibrated non-tacky ultrasonic characteristic that produces a non-tacky wire bond condition on the wire bonding system to be calibrated; (d) determining a calibration factor for the calibrated wire bonding system using the reference non-tacky ultrasonic signature and the calibration non-tacky ultrasonic signature; The method comprising:

2. 2. The method of claim 1, wherein step (a) includes determining a reference ultrasonic characteristic on a reference wire bonding system using application specific components.

3. The method of claim 2 , wherein the application specific component comprises at least one of a wire, a wire bonding tool, and a work piece.

4. 2. The method of claim 1, wherein step (a) includes determining a reference ultrasonic characteristic on a reference wire bonding system using an application specific wire bonding program.

5. 2. The method of claim 1, wherein step (a) comprises determining a reference ultrasonic characteristic on a reference wire bonding system using application specific wire bonding parameters.

6. 2. The method of claim 1, wherein the reference ultrasonic characteristic is a value of a current configured to be applied to an ultrasonic transducer on a wire bonding system to form the wire bond.

7. 2. The method of claim 1, wherein step (b) includes determining the reference non-tacky ultrasonic property by incrementally adjusting an applied ultrasonic property until the non-tacky wire bond condition occurs during a wire bonding operation.

8. 8. The method of claim 7, wherein the non-tacky wire bond condition in step (b) occurs when a predetermined percentage of the wire bonds tested with the applied ultrasonic properties do not adhere to their respective bonding locations.

9. 2. The method of claim 1, wherein step (c) includes determining the calibrated non-tacky ultrasonic characteristic by incrementally adjusting an applied ultrasonic characteristic until the non-tacky wire bond condition occurs during a wire bonding operation.

10. 10. The method of claim 9, wherein the non-tacky wire bond condition in step (c) occurs when a predetermined percentage of the wire bonds tested with the applied ultrasonic properties do not adhere to their respective bonding locations.

11. The method of claim 1 , wherein step (d) comprises determining a difference between the reference non-sticky ultrasonic characteristic and the calibration non-sticky ultrasonic characteristic.

12. The method of claim 1 further comprising: (e) determining ultrasonic characteristic settings for the calibrated wire bonding system using the calibration coefficients.

13. 1. A method for calibrating ultrasonic characteristics on a wire bonding system, comprising: (a) determining a reference ultrasonic characteristic for forming a wire bond; (b) determining criteria out-of-tolerance ultrasonic characteristics that result in an out-of-tolerance wire bond condition; (c) determining, on the wire bonding system being calibrated, out-of-tolerance ultrasonic characteristics that result in out-of-tolerance wire bond conditions; (d) determining a calibration factor for the calibrated wire bonding system using the baseline out-of-tolerance ultrasonic characteristic and the calibration out-of-tolerance ultrasonic characteristic; The method comprising:

14. 14. The method of claim 13, wherein step (a) includes determining a reference ultrasonic characteristic on a reference wire bonding system using application specific components.

15. 15. The method of claim 14, wherein the application specific features include at least one of a wire type, a wire bonding tool type, and a work piece.

16. 14. The method of claim 13, wherein step (a) includes determining a reference ultrasonic characteristic on a reference wire bonding system using an application specific wire bonding program.

17. 14. The method of claim 13, wherein step (a) includes determining a reference ultrasonic characteristic on a reference wire bonding system using application specific wire bonding parameters.

18. 14. The method of claim 13, wherein the reference ultrasonic characteristic is a value of a current configured to be applied to an ultrasonic transducer on a wire bonding system to form the wire bond.

19. 14. The method of claim 13, wherein step (b) includes determining the reference out-of-tolerance ultrasonic characteristic by incrementally adjusting an applied ultrasonic characteristic during a wire bonding operation until the out-of-tolerance wire bond condition occurs.

20. 20. The method of claim 19, wherein the out-of-tolerance wire bond condition in step (b) occurs when a predetermined percentage of the wire bonds tested with the applied ultrasonic property are out of tolerance based on a predetermined criterion.

21. 14. The method of claim 13, wherein step (c) includes determining the out-of-calibration tolerance ultrasonic characteristic by incrementally decreasing an applied ultrasonic characteristic during a wire bonding operation until the out-of-tolerance wire bond condition occurs.

22. 22. The method of claim 21, wherein the out-of-tolerance wire bond condition in step (c) occurs when a predetermined percentage of the wire bonds tested with the applied ultrasonic property are out of tolerance based on a predetermined criterion.

23. 14. The method of claim 13, wherein step (d) includes determining a difference between the reference out-of-tolerance ultrasonic characteristic and the calibration out-of-tolerance ultrasonic characteristic.

24. 14. The method of claim 13, wherein the out-of-tolerance wire bond condition is a non-tacky wire bond condition.

25. 14. The method of claim 13, wherein the out-of-tolerance wire bond condition is a low shear strength wire bond condition.

26. 14. The method of claim 13, wherein the out-of-tolerance wire bond condition is a low tensile strength wire bond condition.

27. 14. The method of claim 13, wherein the out-of-tolerance wire bond condition is an out-of-tolerance level of wire bond deformation.

28. 14. The method of claim 13, further comprising: (e) determining ultrasonic characteristic settings for the calibrated wire bonding system using the calibration coefficients.

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